Amplifying transmitter



@ct. 9, H4. w P. CARSTARPHEN 3 AMPLIFTING TRANSMITTER Filed Jan. 5, 1944 INVENTOR. William P Cars farphen ATTORNE Patented Oct. 9, 1945 1 il G TRANSMITTER Application January 3, 1944, Serial No. 516,895

9 Claims.

This invention relates to improvements in sound transmitters of the general type employed in connection with telephones, hearing aids, broadcasting and sound detection and transmissions in general.

In the ordinary telephone transmitter, the vibrations of a diaphragm are transmitted to a carbon granule resistor in such a way that their resistance to the flow of an electric current varies with the amplitude of the diaphragm vibrations.

When the pressure increases, the carbon gran- Itis well known that the resistivity of carbon decreases with pressure and that the resistance of a. circuit can therefore be varied by changing the pressure applied to a portion of a circuit conductor containing carbon. property was the basis of the Edison microphone transmitter. The use of carbon granules followed that of the solid carbon microphone element of Edison and is now in common use. The variation in the resistance of a carbon granule resistance element is due in part to the negative pressure resistivity and in part to the fact that the pressure urges the granules into closer contact.

It is evident that the pressure variations due to the impact of the sound waves on the transmitter diaphragm cannot produce any great force variations and that therefore the variations in the current are small.

It is the object of this invention to produce a transmitter of the carbon microphone type in which the variations in the current will be amplified by magnetic means to such an extent that stronger signals willbe produced.-

This invention, briefly described, consists in passing the transmitter'or microphone current through a coil surrounding either a permanent magnet core or a soft iron magnet core in such a way as to vary the magnetic flux in accordance with the amplitude of the transmitter diaphragm vibrations and to position the carbon resistance element between one pole of the electromagnet and an armature so that the increase in the current due to the increased pressure exerted on the carbon resistor will cause an increase in the strength of the magnet with a corresponding increase in the magnetic pull on the armature. This increased pull will produce an increase in the pressure applied' to the carbon resistor element and consequently a decrease in its resistance and an increase in the current. As soon .as the diaphragm reverses so as to reduce the pressure, the current and magnetic pull will also decrease.

Another object is to produce a transmitter of the type described in which the usual carbon granules shall be replaced by granules having a magnetic core coated with carbon, or which are made from a mixture of carbon and iron powder. Such granules are magnetic and when subjected to the action of a magnet they tend to compress or be urged against each other so as to augment the compression due to the vibrating diaphragm.

In order to describe the invention with greater detail and particularly so that it may be more readily understood, reference will now be had to the accompanying drawing in which the invention has been illustrated and in which:

Figure 1 is a transverse section of a transmitter taken on line I-I, Figure 2;

Figure v2 is a diametrical section taken on line 22, Figure 1;

Figure 3 shows a modified form of the invention;

Figure 4 is a diametrical section through a granule formed from a mixture of carbon and iron powder; and

Figure 5 is a section showing a granule formed from a magnetic core with a coating of carbon.

The granules shown in Figures 4 and 5 have been greatly enlarged on the drawing, but are to be of the usual size employed in telephone transmitters.

In the drawing reference numeral l0 designates a cup-like member of insulating material, such as hard rubber, or some suitable plastic and reference numeral ll designates a cover secured to the open-end of member H! by means of a threaded connection i2. A sheet metal dia phragm i3 is positioned against the open end of member all and held in position by means of the cover H, which is provided with an internally extending flange It for this purpose. A U- shaped magnetic strap l5 of soft iron, is positioned in the member so with its ends in the vertical grooves it provided therefor in the walls of member I0 and is secured to the bottom tion' in the magnetic flux from the permanent magnet 43 of the receiver. The operation just described is analogous and almost identical with that of the ordinary telephone transmitter, but

of the latter by means of screws ll. Extending upwardly from the base of member I! is a magnetic core l8 which may be made from soft iron, or from hard steel in the form of a permanent magnet. If a permanent magnet is employed, it is preferably of the type comprising an aluminumalloy, which is marketed under the trade name of Alinco," or some other alloy suitable for permanent construction.

Core i3 may be secure to strap II by means of a threaded connection l9, as shown in Figure 12, or in any other suitable way. Surrounding the core I8 is a coil of wire which has been designated by reference numeral 20. This coil is wound in the form of a spool in the ordinary manner, the spool being so constructed that it can be readily positioned on the core during the manufacture. Reference numerals 2| and 22 designate the ends of the spool. Secured to the top of the core is a cup 23 of nonmagnetic material. A carboir -plate 24 is positioned in the bottom of cup 23 and one end of the wire 2| is electrically connected with plate 24., Positioned in the cup and resting on plate 24 is a large number of carbon granules 25. On top of the granules is a carbon plate 26 on which is supported a soft iron armature 21. This armature terminates in a conical portion 23 against the apex of which the diaphragm l3 rests. Secured to the inner surface of one of the vertical arms of the U- shaped member I is a plate 29 of insulating material. This has been shown as held in place by means of screws 30 and 3|. A spring 32 is secured at oneend to the insulating member 29 by means of a screw 33 and the upper end of this spring is provided with an opening through which the center portion of the armature 21 extends. A screw 34 is threadedly connected with the insulating plate 29 and extends through an opening 35 in the strap IS. The inner end of screw 34 engages the surface of spring 32 and by means First, the current that flows through the carbon granules also flows through the coil surrounding the core i8 and if the latter is a permanent magnet, it causes a variation in the magnetic flux. Second, this transmitter is provided with an armature 21 which is acted upon by the magnetic flux from the permanent magnet l3 and therefore when the diaphragm moves downwardly, when viewed as in Figure 2, it increases the compression on the carbon granules thereby, producing an increased current, this increased current will further increase the magnetic flux and the resultant pull on the armature, thereby further compressing the carbon granules allowing more current to now which increases the magnetism producing further compression.

At this place it will be pointed out that where core I 8 is in the form of a permanent magnet, the battery must be so connected that thecurrent in coil 20 will increase the magnetism so that an increased current will produce an increased magneticpull. If core is is of soft iron,

- such as a bundle of very fine soft iron wires or of this screw the pressure exerted by the spring on the armature 21 can-be adjusted.

A wire 36 i connected with the spring 32 and terminates in the receiver hook switch contact 31. The other contact 38 of this switch extends to one pole of a battery 39. The coil 20 terminates in a wire 40 that is connected to one ter-, minal of the primary winding 4! of a transformer from which conductor 42 extends to the battery. The secondary 43 of the transformer is connected to the winding 44 of a telephone receiver whose diaphragm has been designated by reference numeral 45. A spring 431s connected with the receiver hook 41 the receiver is oil from the hook, the switch is closed.

Let us now assume that with the parts arranged as shown in Figure 2 and described above,

from electrolytic iron powder which has been compressed, the direction of current flow in coil 20 is immaterial.

From the description just given it will be apparent that whenever the diaphragm moves downwardly so as to compress the carbon granules and thereby reduce the resistance of the circuit, due to the better contact aiforded between the particles whenthus compressed and due further more to the characteristic of carbon which decreases its resistivity with pressure, an increased current will flow through the coil 20, thereby increasing the pressure which, in turn, increases the current and this amplification is transmitted through the transformer to the receiver. As soon as diaphragm l3 moves upwardly, the pressure on the carbon granules immedi-.- ately decreases, thereby increasing the resistance and decreasing the current.

Due to the fact that the pressure responsive resistance is in series with coil 4|, the battery 39 and the magnet coil iii, the variations in resistance, due to'the pressure variations, are small compared to. the resistance of the entire circuit. The variations in resistance due to the action of the diaphragm causes a large increase in the resistance when the diaphragm moves upwardly, when viewed as in Fig. 2, and this removes any possibility of the parts locking due to the progressive increase in current resulting from the in such a way that when decrease in the resistance produced by the magnetic attraction.

Particular attention is called to the cons ction just described in which the current through the carbon microphone transmitter causes a variation in the compression forces so as to produce a sound of varying intensity is emitted adjacent from the battery 39 flows through the spring 32.

through the carbon granules through coil 20 and through the primary 4| and the variations in this current due to the variations in the pressure, ex-

on the carbon granules, produce an induced current in the secondary 43 which causes a variadiiferstherefrom in these important particulars. 7s

a corresponding variation in the resistance of the carbon element of the circuit. By means of this interaction an amplifying function is obtained.-

Inthe construction shown and described above, ordinary carbon granules can be employed because the magnetic attraction of the permanent and electromagnet acts on the armature 21 to produce the result described.- Better and more marked results can be obtained, however, by substituting for the ordinary carbon granules, other granules having magnetic properties. These granules may be made from a mixture of carbon powder and powdered iron, as indicated in Figure 4, such powder mixture being formed into granules by submitting the powder to pressure in uitable molds. Another way of producing these V 50 and covering them with a layer M of carbon.

This layer may be applied in several difierent well known ways, as, for example, it may be covered with a hydrocarbon oil and carbonized or subjected to heat in an atmosphere containing carbon or subjected to an electrolytic plating operation by means of which carbon will be electrolytically deposited thereon.

When granules having magnetic propertie are employed in place of the pure carbon granules, it is evident that the magnetic attraction will be exerted on the separate granules, as well as on the armature 21. In fact with magnetic granules it is possible to replace the soft iron armature}? with one made from aluminum or other nonmagnetic material. In either case the member corresponding to armature 21 should be conductive so that current may fiow from the spring to the carbon plate 26.

Since carbon has the property of reducing its resistance-when subjected to pressure, it is possible to dispense with the carbon granules and allow the two plates 24 and 26 to come into direct contact as shown in Figure 3. Inthis case the cup 23 can be made very shallow. With the construction shown in Figure 3, the magnetic attraction is exerted on the armature 21 and this varies the compressive forces applied to the carbon in a manner analogous to the well known Edison carbon microphone transmitter.

The U-shaped member I forms a part of the magnetic circuit, another part of which is .formed by the diaphragm I3, which is preferably from magnetic material. Thin sheets of insulating material like that designated by reference numeral 52 in Figure 2 are interposed between the diaphragm l3 and the ends of the strap IE, or other suitable means is provided for electrically insulating the diaphragm from contact with any current carrying parts.

The transmitter described above and shown on I the drawing can be employed in ordinary telephone circuits or in any other sound transmitting system where amplification is desired. It is believed to be of particular importance in connection with hearing aids for slightly deaf people, because this amplifying property makes it possible to dispense with the ordinary electronic amplifying tubes now incorporated in such hearing aids. With this simple construction amplification can be obtained without complicated and expensive mechanism, thereby reducing the first cost and reducing the subsequent cost of upkeep.

Although applicant cannot, at this time, enumerate all uses to which this invention might be put, it is to be unlerstood that he does not desire to be limited strictly to the uses specified.

Although the invention has been illustrated of certain shape and size, it is, of course, to be understood that this is merely for the purpose of description and that the invention is entirely independent'of the specific shape and size in which it is embodied.

Having described the invention what is claimed asnewis:

1. A sound transmitting and reproducing device comprising, in combination, an electromagnet, an armature comprising an assemblage of granules containing carbon and iron, means for circulating a direct current through the armature and the winding of the electromagnet, and a sound responsive device operatively associated with the armature for varying the pressure therecombination; an electromagnet comprising a cpre and a magnetizing coil, an armature operatively associated with the core and spaced therefrom,

a pressure responsive resistance element positioned between the core and the armature to be compressed by the latter when it is attractedby the electromagnet, an electric circuit comprising the resistance element and the magnet coil in series, a source of direct current in series in the circuit, and means comprising a sound responsive diaphragm for moving the armature to vary the compression of the resistance element.

3. A sound transmitter and amplifier comprising a base, a magnetic core carried-thereby, an armature carried by the base and spaced from the magnetic core, a pressure responsive resistance element positioned between the core and the armature in position to be compressed when the armature moves towards the core, a magnetizing coil enclosing the core, a source of direct current,

a circuit comprising the pressure responsive resistance, the current source and the wire coil forming a current path, and means independent of the action of the magnetism from the core and coil for moving the armature towards and away from the core to vary the resistance of theresistance element, whereby when the armature approaches the core, the current in the coil will increase, producing a greater pressure.

4. An amplifying sound transmitter comprising a base, a diaphragm supported thereon for vibra tion in response to sound waves, an electromagnet comprising a magnetizing core and acoil supported on the base, the end of the core being spaced from the diaphragm, a pressure responsive resistance element so positioned between the core and the diaphragm that the latter exerts a 'betweenthe core and the diaphragm and so associated with the core that the magnetic pull thereon will compress the element and reduce its resistance, thereby increasing the flow of current and the magnetic pull. 5. A sound amplifying transmitter comprising, in combination. 'a base, a magnet'core secured thereto, a magnetizing coil surrounding the core, an armature movably connected with the base and spaced from the core, a resistance element having a negative pressure resistance characteristic, positioned between the armature and an end of the core, said element comprising carbon granules, means comprising a sound responsive diaphragm for urging the armature towards the core and against the carbon granules, an electric circuit comprising the magnetizing coil, the carbon granules and a source 'of direct current in series, and means comprising the diaphragm for moving the armature in response to sound waves, whereby the current in the magnet coil will be varied, producing a corresponding variation in the force acting on the armature.

6.- In a sound trari smitter an amplifying ele-.

ment comprising acore of magnetic material, a

a pressure responsive resistance element positioned between the armature and an end of the core, said element comprising granules containing carbon and a magnetic material, means comprising a sound responsive diaphragm for exerting a pressure on the carbon granules, an electric circuit comprising the carbon granules, and a source of direct current in series, and means comprising the diaphragm connected with the base and-with the resistance element for varying the pressure on the granules in response to sound waves, whereby the current in the magnet coil will be varied producing a corresponding variation in -the magnetic force acting on the granules.

8. A sound amplifying device comprising, in

, combination, a base, a core secured thereto, a

diaphragm connected with the base andspaced from one end of the core, a magnetizing coil surrounding the core, a resistance element positioned between the coreand the diaphragm, said element comprising an assemblage of granules formed from carbon and iron, means positioned between the diaphragm and the granules for exerting a pressure on the granules and for varying the pressure in accordance with the vibrations of the diaphragm in response to sound waves, anda source of direct current, a circuit comprising the resistance element, the magnetizing coil andthe source of current in series, whereby the varying resistance of the resistance element, in response to diaphragm vibrations, will produce a correspending variation in the currentand in the magnetic flux, whereby the action of the latter on the magnetic granules will vary the rmistance inversely'with the current.

9. An amplifying device. comprising, in combination, a permanent magnet core, a coil surrounding the core, a pressure responsive resistance element comprising granules having an iron core covered with carbon positioned adjacent the core, means responsive to the flux of the magnet for exerting a compressive force on the resistance element, which varies with the intensity of the magnetic flux, a circuit comprising a source of direct current, the resistance element and the coil in series, means independent of the magnet for varying the compression of the resistance element in accordance with sound waves, whereby the current in the circuit and the magnetic flux will vary. WILLIAM P. CARSTARPHEN. 

